U.S. Pat. No. 5,460,317 is a classic reference on friction stir welding. In particular, it cites the use of a non-consumable probe comprised of a material which is harder than the workpieces being joined. (The probe should remain hard at elevated temperatures which are sufficient to soften the workpieces.) In a typical application, the method is used for butt welding. The probe is rotated relative to the workpieces and is pressed against the workpieces at the juncture between two workpieces. Friction between the probe and the workpieces generates heat which plasticizes the workpieces and permits the probe to enter.
The workpieces are not melted by this procedure, but are softened (i.e. plasticized) sufficiently for flow to occur. Oxidation problems are thus avoided. After the probe has been plunged into the joint between the workpieces, and the portions of the workpieces in the immediate vicinity of the probe are plasticized, the probe is translated along the interface between the two workpieces, thereby thoroughly intermingling the two workpieces. It is noted that the plasticized material flows around the axis of the rotating probe whereby thorough mixing occurs.
This patent also teaches repair of a crack by plunging a rotating probe into the workpiece at the site of a crack, and translating it along the crack. Plasticized material on both sides of the crack is thoroughly intermingled to repair the crack.
U.S. Pat. No. 5,971,252 presents a process to repair voids in an aluminum alloy, particularly a friction stir weld in an aluminum alloy. For an elongated void, the method includes machining a trough that subsumes the void. A strip of material having the same composition as the alloy to be repaired and having sufficient volume to fill the trough is then placed in the trough. A friction stir welding tool is then traversed longitudinally through the strip whereby the strip fills the trough and is bonded to it. The strip of material does not need to be machined precisely to the shape of the trough, but it has sufficient volume to fill the trough.
U.S. Pat. No. 5,975,406 teaches a method to repair a void in an aluminum alloy plate, particularly a void resulting from friction stir welding. The method includes machining the void to provide a tapered bore through the plate. Grooves and ridges are formed on the sidewall of the tapered bore. A consumable tapered plug of the same aluminum alloy as the plate is inserted into the bore and is rotated as the plug is pressed into the bore. Friction welding occurs at the interface between the plug and the bore and rotation is continued to produce a strong bond consisting of refined and recrystallized fine metal. The weld is then allowed to cool. Subsequently, portions of the plug (referred to as stabs) on each side of the plate are machined away.
U.S. Pat. No. 6,213,379 is directed toward friction stir welding in which requirements of the job make it necessary for all equipment to be located on one side of the work piece. Friction stir welding is done by a plug which is held in a chuck turned by a motor. The proximal end of the plug, which is held by the chuck, has a smaller diameter than the distal end of the plug. The plug may taper from its smaller diameter at the proximal end to its larger diameter at the distal end. The plug is inserted from the back side of the workpiece (on the opposite side from the chuck and motor) and it is pulled toward the chuck. This method, friction plug pull welding, is directed toward repair of tanks such as the propellant tanks for the space shuttle.
U.S. Pat. No. 6,230,957 teaches the use of friction stir welding to repair fusion welds. Passing a friction stir welding tool through a fusion weld converts the cast microstructure to a fine grained, dynamically recrystallized microstructure showing higher strength, ductility, toughness and resistance to weld cracking.
U.S. Pat. No. 6,422,449 presents a method of repairing a friction stir weld by means of inert gas arc welding.
U.S. Pat. No. 6,638,641 provides teaching concerning the exact shape of a rotating member for stir welding, and a recess in a workpiece. In particular, conic sections of rotation are employed for both the rotating member and the recess. These may be paraboloids, spheroids, or conoids. The shape of the rotating member may differ slightly from that of the recess to minimize the torque needed to begin the friction welding process.
The teachings of the aforementioned patents are hereby incorporated into the present application by reference thereto.